Time delay relay



Dec. 12, 1939. SLEDD 2,183,412

TIME DELAY RELAY Filed Dec. 16, 1938 Ir'wverwtorw Mabvin B. Sledd,

b k TJ y His Attorwwey.

Patented Dec. 12, '1939 UNITED STATES TIME DELAY RELAY Marvin B. Sledd,Schenectady, N. Y., assignor to General Electric Company, a corporationof New York Application December 16, 1938, Serial No. 246,181

Claims.

My invention relates to time delay relays of the type wherein the delayis determined by the time required for a capacitor to lose a certainamount of charge. Such a relay has been described and 6 claimed in thecopending application of Elbert D. Schneider, Serial No. 155,518, filedJuly 24, 1937, assigned to the same assignee as the present application.With that relay it was found that under certain conditions, such as whenit was 10 used to control loads that produced considerable drop in thevoltage of the line supplying the relay there was a tendency for theload controlling contacts of the relay to chatter at the end of thetiming period. It is an object of my invention to provide an improvedform of the relay disclosed in the' aforesaid Schneider applicationwhich will avoid any tendency toward chattering.

My invention will be better understood from the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

In the single figure of the drawing which is a circuit diagram showing asomewhat simplified form of the relay disclosed in the aforesaidSchneider application together with an embodiment of my invention, I and2 represent the leads of a source of alternating current supply which,for example, may be a 60 cycle lighting circuit at 220 volts. Connectedacross the source is the voltage divider 3 which is shown as comprisingthe resistor 4 and the potentiometer 5. The electron discharge device Ihaving the anode 8, the control grid 9 and the cathode I I] is arrangedto be energized from the source I, 2, the cathode being shown connecteddirectly with the lead 2 through the single pole, single throw switch II and the anode being shown connected through the winding of the relayI2 with the other lead I of the source. The grid 9 connects with themovable contact 6 of the potentiometer through the capacitor 20 which isshunted by the resistor 2| forming a leakage path through which thecapacitor may lose its charge at a predetermined rate. The cathode ID,in addition to its connection with the lead 2 through the switch I I,has a permanent connection with the lead I through the resistor 22. Theapparatus thus far described is essentially that disclosed and claimedin the aforesaid Schneider application.

In the drawing of the present application, I

have shown the relay I2 provided with a movable contact 23 arranged whenthe relay is energized to close the load circuit 24 including anysuitable load device represented at 25. This load 5 circuit connectswith the leads I and 2 whereby the closing of the load circuit by therelay I2 may tend to produce a drop in voltage between those leads. Therelayv I2 is provided with another movable contact 26 and thecooperating fixed contacts 21, which latter connect through the ll leads,28 with the capacitor 20 and the point 29 connecting with the grid andwith one side of the leak resistor 2I. The movable contact 26 is soarranged that when the relay I2 is operated the circuit controlledthereby between the capaci- 10 tor and the point 29 is opened.

Assuming the switch II to be in its open circuit position asillustrated, in which case no current flows in the anode-cathode circuitof the discharge device 'I and the relay I2 is deenergized, there willbe a grid current flow during these half cycles, which for conveniencewill be termed the negative half cycles, at which the lead I is negativewith respect to the lead 2. This grid current is that due to thepotential difierence 20 between the potentiometer contact 6 and the leadI and charges the capacitor 20 in such a manner that the side thereofwhich connects with the 'grid is negative, it being noted that the onlyconnection of the cathode with the source at 25 this time is thatthrough the resistor 22 to the lead I. Thus, while the switch II isopen, the negative half cycles of the supply voltage keep the capacitor20 in a charged condition.

When the switch II is closed the anode-cathode 30 circuit of the deviceI is closed whereby the device may function to pass current during thepositive half cycles to operate the relay I2 under the control of thegrid 9. Closing of the switch II also serves effectively to transfer theconnec- 35 tion of the cathode from the lead I to the lead 2, it beingnoted that the connection of the cathode with the lead 2 is ofnegligible resistance. The charge formerly given to the capacitor 20maintains the grid 9 sufiiciently negative to prevent 40 current flowthrough the device 1 until the charges on the plates of the capacitorhave had time to equalize through the resistor 2I, or at least to becomereduced to such a value that the device I will pass current sufiicientto cause an 45 operation of the relay I2. After the operation of therelay I2, the switch II may be opened at which time the relay will moveto open circuit position and the capacitor 20 will again become chargedby the grid current of the device I during 50 the negative half cycles.It will thus be seen that after the closing of the switch II the relayI2 will be operated only after the'lapse of a pre determined timeinterval. The duration of this interval depends upon various factorssuch as the capacitance of the capacitor, the resistance of the resistorin shunt therewith and the setting of the potentiometer. Adjustment ofthe latter provides a convenient method of varying the time delayinterval as desired,

In the above described operation of the apparatus I have not taken intoconsideration the effect of the operation of the relay l2 upon the gridcircuit of the device 1 nor the effect on the line voltage of closingthe load circuit 24. It has been found that in some cases the closing ofthe load circuit at the end of the timing interval has caused the relayI2 to chatter. This is probably due to the fact that the closing of theload circuit produced a drop in the voltage supplied to the dischargedevice I so that the relay 1! became deenergized sufliciently to reopenthe load circuit. The load thus being removed from the supply leads thevoltage supplied to the discharge device was immediately restored whencethe device again passed sufficient current to re-operate the relay toreclose the load circuit. The above sequence of operation may continueto repeat itself until such time that the negative bias supplied to thegrid by the capacitor 20 is-insufncient' to prevent the operation of therelay.

The additional contacts 26 and 21 of the relay l2 being arranged to openthe connection between the capacitor and the grid when the relayoperates serves to reduce or to'remove the biasing effect of thecapacitor on the grid of the discharge device for it will be seen thatupon the first operation oi the relay l2 the connection between thecapacitor and the grid is opened thus removing whatever negative bias isbeing supplied by the capacitor to the grid. This removal of thenegative bias supplied to,the grid causes an increase in the currentthrough the relay l2, and this increase prevents the relay l2 frombecoming sufficiently deenergized by the "drop in voltage to reopen theload circuit. Chattering is thus avoided.

What I claim as new and desire-to secure by Letters Patent of the UnitedStates, is:

1. A time delayv relay comprising a voltage divider arranged to be.connected across a source of alternating current supply, a gridcontrolled electron discharge device having its anode and cathodeconnected with spaced points of said divider, a current responsivedevice in one of sad connections, a capacitor connected between saidgrid and a point of said divider between said spaced points, a switch insaid cathode connection, a resistor connected between said cathode andsaid divider at a point of the divider on the opposite side of saidcapacitor connection from said first mentioned cathode connection andmeans responsive to the operation of said current responsive device forreducing the efiect of said capacitor on said grid.

2. A time delay relay comprising a source of supply of alternatingcurrent, a grid controlled electron discharge device having its anodeand cathode connected to be energized irom said source, a currentresponsive device in one or said connections, a switch in said cathodeconnection, means connected with said cathode and grid and operable whensaid switch is open for producing 1 vider arranged to be connectedacross a source of alternating current supply, a grid controlledelectron discharge device having its anode and cathode connectedwithspaced points of said divider, a relay in one of said connections, acapacitor provided with a high resistance shunt connected between saidgrid and a point of said divider between said spaced points, a switch insaid cathode connection and a resistor connected between said cathodeand said divider at a point thereof on the opposite side of saidcapacitor connection from said first mentioned cathode connection, saidrelay having cooperating contacts arranged to -remove the efie'ct oi!said capacitor on said grid.

4. A time delay relay comprising a source of supply of alternatingcurrent, a grid controlled electron discharge device having itsanode andcathode connected to be energized from said source, a relay in one ofsaid connections, a switch in said cathode connection, means connectedwith said cathode and grid and operable when said switch is open forproducing a grid current during the negative half cycles of thealternating current, and a capacitor having a high resistance shunt inseries with said grid arranged to be charged by said grid current, saidrelay having cooperating contacts operative to open the connectionbetween the capacitor and the grid.

5. A time delay relay comprising a voltage divider arranged to beconnected across a source of alternating current supply, a gridcontrolled electron discharge device having its anode and cathodeconnected with spaced points of said divider, a current responsivedevice in one of said connections,- a capacitor connected between saidgrid and-a point of said divider between said spaced points, a switch insaid cathode connection, a resistor connected between said cathode andsaid divider at a point thereof on the oppo'- site side of saidcapacitor connection from said first mentioned cathode connection, arelay provided with a plurality of movable contacts connected in theanode circuit, a load circuit connected to be supplied from said. sourceand to be controlled by one of said movable contacts and 'means wherebyanother of said movable contacts controls the connection between saidcapacitor and said grid.

- MARVIN B. SLEDD.

